The invention relates to the field of variable gain amplifiers, and particularly relates to the field of variable gain amplifiers for high frequency signals such as radio frequency (RF) signals.
For certain applications, it is desirable that variable gain amplifiers provide a fixed gain change in decibels responsive to an incremental change in control voltage. This feature is generally known as being linear in dB. It is also desirable that variable gain amplifiers be economical yet accurate and precise, and that they operate at a stable temperature throughout the gain range.
There is a need for an improved variable gain amplifier for high frequency signals that is linear in dB and is temperature stable.
The invention provides a variable gain amplifier system for radio frequency signals. The amplifier system of the invention provides a relatively constant gain change in decibels responsive to an incremental change in control voltage. The system includes two or more cascaded gain stage amplifiers, and each gain stage amplifier is adjustable between a first gain setting and a second gain setting.
In an embodiment, the invention includes three gain stage amplifiers. The first gain stage amplifier has an input, an output, a first reference signal input and second reference signal input. The second gain stage amplifier has an input that is coupled to the output of the first gain stage amplifier, an output, a first reference signal input and a second reference signal input. The third gain stage amplifier has an input that is coupled to the output of the second gain stage amplifier, an output, a first reference signal and a second reference signal.